The possible role of psychosocial factors in the aetiology of insulin dependent (Type 1) diabetes mellitus (IDDM) is being investigated in association with the Barts-Windsor Prospective Family Study. Using the life-events and difficulties schedule (LEDS) of Brown and Harris, we have shown an increased frequency of severe life-events in diabetic family members prior to disease onset when compared to sibling controls. We propose to develop this study by examining in family members the temporal relationship between stressful life events and the appearance of certain immunologic markers (particularly complement fixing and 'conventional' islet cell antibodies (ICA) known to be predictive of the onset of IDDM in genetically susceptible individuals. We also propose to develop our present study in middle-aged diabetics of the relationship between psychosocial factors and the complications of diabetes. A prospective study will be carried out by re-examining the original cohort of diabetics by standardized procedures and studying the relationship between past stressful life-events and difficulties and the occurrence of diabetic complications. The relationship of copingbehaviour and socio-economic-ethnic factors to the risk of developing diabetic complications will also be examined. Information from these studies of the psychosocial aspects of diabetes will hopefully be of value in the planning of preventive strategies for the onset of the disease or its complications.